3GPP (3rd Generation Partnership Project) is a project that is intended to study and formulate specifications of a mobile communication system based on a network that is upgraded from W-CDMA (Wideband-Code Division Multiple Access) and GSM (registered trademark) (Global System for Mobile Communications). Currently being studied under 3GPP, with the advance of the third-generation radio access technology (hereinafter referred to as “LTE (Long Term Evolution)” or “EUTRA (Evolved Universal Terrestrial Radio Access)” and the use of a wider frequency bandwidth, is a mobile communication system (hereinafter referred to as “LTE-A (Long Term Evolution-Advanced)” or “Advanced-EUTRA”) that permits even higher data transmission and reception.
As a communication scheme in LTE, 3GPP is studying, for a downlink, OFDMA (Orthogonal Frequency Division Multiple Access) that performs user-multiplexing using mutually orthogonal subcarriers and SC-FDMA (Single Carrier-Frequency Division Multiple Access) for an uplink.
As a communication scheme in LTE-A, 3GPP is studying OFDMA for the downlink and for the uplink, an introduction of Clustered-SC-FDMA (Clustered-Single Carrier-Frequency Division Multiple Access, also referred to as DFT-s-OFDM with Spectrum Division Control or DFT-precoded OFDM) in addition to SC-FDMA.
In a radio communication system, a communication area may be expanded by introducing a cellular structure to arrange in a cell-like fashion a plurality of coverage areas covered by base station apparatus. Although even a mobile station apparatus in a cell edge (cell end) region communicates without being interfered by using different frequencies between adjacent cells (sectors), frequency usage efficiency is problematic. In LTE, the frequency usage efficiency is substantially increased by using the same frequency repeatedly in each of the cells (sectors). However, a mobile station apparatus in the cell edge region is likely to be affected by interference from an adjacent cell, and communication quality is degraded. This entails reducing or suppressing interference to the mobile station apparatus in the cell edge region.
Currently being studied in LTE-A as a method of reducing or suppressing interference to the mobile station apparatus in the cell edge region is a Coordinated Multi-Point Transmission/Reception (COMP) that performs interference coordination to cause adjacent cells (adjacent transmission and reception points) to coordinate each other. The word point herein refers to a transmission point (transmission station apparatus) of a signal and a reception point (reception station apparatus) of a signal. For example, the point may be a base station apparatus. Also, the point may be a mobile station apparatus. Also, the point may be a relay station apparatus. The point may be RRH (Remote Radio Head) as an upgraded antenna facility.
In coordinated communications, orthogonal resources alone of a uplink demodulation reference signal (DMRS: Demodulation Reference Signal) of LTE are insufficient to ensure orthogonality between the cells (transmission and reception points). Currently being studied is an increase in the orthogonal resources of DMRS that may be achieved by changing the frequency resource allocation of DMRS in a frequency spectrum from localized resource allocation to distributed resource allocation (for example, comb spectrum arrangement at two-subcarrier intervals such as a sounding reference signal (SRS: Sounding Reference Signal) (Non Patent Literature 1).
Disclosed further in the coordinated communications are a scenario where cell IDs (physical layer cell identities) different among a plurality of points are set, and a scenario where a common cell ID is set (Non Patent Literature 2).